German Shell Case 1916 - Mystery Marking?

[Alpini]

...also thought about it, but in Ottoman alphabet the "mim" looks a bit different, at least here:

Osmanische Sprache – Wikipedia

de.wikipedia.org

But also the "he" doesn't fit very well.

 

[Hoeksel]

I am now convinced the meaning is "Rha.Ayn" (Ottoman) and is indeed a phonetic reference for Rheinmetall.